1. Field of the Invention
This invention relates to a magnetic fluid sealing device used in hard disk drives and the like.
2. Description of the Related
Heretofore, a conventional magnetic fluid sealing device has been constructed as shown in FIG. 9. That is, as shown in FIG. 9, held between the inner surfaces of a pair of pole pieces 21 made of magnetic material in doughnut-shaped disk form is a doughnut-shaped magnet 22 having a greater inner diameter than that of the pole pieces, the assembly being fixed at its outer periphery to a housing 25, and a rotatable shaft 24 of magnetic material is inserted in the central hole, with magnetic fluid 26 held in the gaps defined between the rotatable shaft 24 and the front end surface of the pole pieces 21 opposed thereto.
In the magnetic fluid sealing device described above, however, the relatively high rotational speed of the rotatable shaft 24 throws the magnetic fluid 26 outwardly to decrease its amount or lower its life, or the magnetic fluid 26 flows out onto the outer surfaces of the pole pieces 21 to contaminate the surroundings.